Digital data transmission across an analog channel is used in displays, servers, data storage, and wireless internet, and may be performed using various modulation schemes, in which an analog signal is modulated according to the data content, i.e., bits of a digital data stream, to be transmitted across the channel. For example, the modulation may involve non-return-to-zero (NRZ) coding.
Referring to FIG. 1, in a conventional receiver, the input c(t) from the channel is, at each unit interval (UI), compared, in an act 110, to a reference signal voltage or threshold value value Vth. If the input exceeds the threshold value Vth, then the data value d(n) at the current unit interval is set, in an act 115, to 1; otherwise it is set, in an act 120, to 0. Referring to FIG. 2, a well-formed data waveform 210 modulated using NRZ coding with the binary pattern ‘1100’, results, in the sampled waveform 215, in two samples P1, P2 exceeding the threshold value and two samples P3, P4 below the threshold value, which results, at the output of the comparator 220, in a digital output stream 225 having two ones followed by two zeros.
Referring to FIG. 3, after an NRZ waveform representing the bit stream ‘0001011111101000’, preceded and followed by some number of zeroes, is transmitted through a channel producing inter-symbol interference or otherwise distorting the transmitted waveform, the received waveform 310 may appear as illustrated and may lack sharp transitions between levels corresponding to 0 and 1, as, for example, illustrated in FIG. 2 for the well-formed waveform 210. Referring to FIG. 4, this may result in errors at, for example, the points in the received waveform circled with dashed lines. Thus, there is a need for a system and method for receiving, e.g., converting to a digital bit stream, a signal received at the output of an imperfect channel.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.